Since the invention by the applicant more than 25 years ago, diamond cutting tools known as diamond knives have received worldwide acceptance as an unsurpassed cutting tool for the preparation of ultrathin sections for microscopic examination, precision machining and delicate surgical operations and have opened up important new fields.
As disclosed in U.S. Pat. No. 3,060,781, the diamond knife consists of a body of single-crystal diamond which has been cut, abraded and polished by special techniques to yield a wedge-shaped facet that, in the most favorable cases defines a stable and uniform cutting edge having a thickness of only 0.001 to 0.01 micron.
Diamond is the hardest substance known and is composed of carbon atoms arranged in sheets of hexagonal puckered rings stacked one above the other closely together with a spacing of only 2.06 Angstrom units. The strong fourfold covalent bond between the carbon atoms together with a unique symmetrical orientation account for the exceptional properties of the diamond. It is this combination of layered structures in the naturally occurring diamond which makes it possible literally to "dissect out" preformed unit layers of still very strongly bonded sheets to form the desired ultrasharp stable cutting edges of molecular dimensions.
However, the difficulties encountered during the past decades, even by the most skillful workers, in reproducibly making diamond cutting edges of satisfactory quality can be ascribed to two major problems which are:
(1) The inherent complexity of a natural diamond which not only consists of the crystalline carbon layers but also features a large number of other atoms such as nitrogen platelets included in the lattice and making up to 0.3% of the type I diamonds most commonly occurring. There are also numerous associated dislocations and defects in the crystalline diamond lattice. This microscopic complexity of the diamond becomes a preponderant factor in making it difficult to dissect out its unit layers to form a cutting edge.
(2) Up till now all of the abrading and polishing methods utilized are essentially mechanical chipping, fracturing and grinding processes which unavoidably disrupt the periodic crystalline lattice of the diamond. In fact extensive studies by X-ray diffraction, electron diffraction and related polarization optical analysis reveal that the primary ultrasharp diamond knife cutting edge has a so-called mosaic structure not unlike "cracked ice" when compared to the uniform smooth and cohesive "ice sheets" corresponding to the original crystalline diamond lattice.
(3) When the diamond knife is "sharpened" on a diamond wheel charged with fine diamond powder at high speeds, the heat generated may be high enough (e.g. 1200.degree. C.) to "graphitize" the diamond in the presence of atmospheric oxygen thereby chemically modifying and degrading the diamond structure.
As disclosed in U.S. Pat. No. 4,084,942, ultrasharp diamond edges and points which are usable as cutting instruments and as high intensity point sources for the emission of electrons, ions and other radiation are produced from ultrafine diamond powder by the application of high pressure and high temperature in an ultrahigh vacuum or inert atmosphere to avoid oxidation of the diamond powder. As a monocrystalline diamond knife is used as a pattern for the mold used in producing polycrystalline diamond knives from ultrafine diamond powder, any imperfections in the monocrystalline master pattern are carried over into the polycrystalline replica. Moreover, even though ultrafine diamond powder is used in molding polycrystalline diamond knives, the surface obtained is not as uniform, smooth and cohesive as that of the original crystalline diamond lattice.